Thick, billowing smoke rolled across Roanoke on Thursday as fire gutted a nearly century-old downtown warehouse while firefighters watched, helpless to save the old brick building.

The fire apparently broke out about 2 p.m. in the basement of the building in the 300 block of Salem Avenue Southwest, which served as a warehouse for Roanoke Electric Zupply. Firefighters chain-sawed their way through bay doors to get in, but were driven out by intense fire and smoke.

Twice, loud bells sounded to clear the firefighters out.

The fire was classified as a two-alarm blaze, but it was briefly upgraded to three alarms, which increases the number of firefighters and amount of equipment at the scene.

Roanoke County brought its air truck to refill air tanks, while firefighters from Salem and Vinton were on standby to help on calls elsewhere in the city.

After about an hour, firefighters realized they could do little to save the building and turned efforts toward saving the building next door. But fearing the burning warehouse might collapse, they cleared fire trucks from the front of the building and emptied a city parking lot next door of government vehicles, including police cars.

Roanoke police officers rushed to wheel away bicycles stored in a shed on the edge of the parking lot. Roanoke Gas and American Electric Power workers shut off utility lines, which interrupted electricity supply in the area.

As the fire intensified, fingers of smoke seeped through the bricks, showing signs of a possible collapse. Flames broke out, engulfing the front of the building and then shooting through the roof.

"The fire was just bigger than we could handle at any time," said Roanoke Fire-EMS Deputy Chief Winston Simmons.

The building stood through the afternoon, but it was destroyed nonetheless and was expected to burn through the night.

Fire crews were, however, able to keep the flames from entering the building next door, which is owned by Roger Lilly and houses Five Star Fab & Fixture and J. Berna Sales Co. Thermal imaging cameras helped firefighters know where to train water against the walls, keeping burning ceiling joists from spreading the flames.

Inside that building, it was "heavy, pushing smoke," Roanoke Fire-EMS Capt. Todd Stone said. Despite the lack of fire damage, Lilly's building sustained water damage when the basement began to flood about 10 p.m. Water that filled the burning building's basement flowed through a hole in the wall.

At the height of the fire, smoke poured down Salem Avenue, limiting vision to a few feet as it billowed past nearby businesses. Workers shut windows and stuffed floor mats against doors in an effort to keep out the acrid smoke.

"We're trying to keep working, but it's burning our eyes," said Joe Lambert, a mechanic at Bumpers Auto & Towing. "I got to give it to them firefighters. They run in there like it wasn't nothing."

The two-story warehouse stored electrical supplies such as conduit and light fixtures, said businessman Bob Zimmerman, who has owned the building about a year and a half. The building previously housed the Furniture Medic until the business moved down the street in 1997.

Zimmerman solemnly watched the fire from the sidewalk. He said he didn't have insurance for the building.

"About 25 years of collection here," he said.

The fire attracted many onlookers, including some with cameras and others who brought their children to watch. City Manager Darlene Burcham walked over, she said, to show her support for the public safety personnel. As the afternoon grew colder, she donned a warm fire department jacket.

Baron Gibson, a city fire lieutenant who was off duty Thursday, had just picked up his 8-year-old daughter from school when he noticed the smoke and drove downtown to take a look.

Kayla Gibson clutched her father's hand with a worried look.

"This is getting scary, Daddy," she said.

A short time later, 6-year-old Tony Brewer sat on his father's shoulders and watched with wide eyes.

"It's really burning," Tony said. "They're going to run out of water."

Ronald Brewer assured his son: "They're not going to run out of water, baby."

Firefighters poured millions of gallons onto the fire from all angles, including from above by ladder. But the construction of the building contributed to its destruction - the warehouse, built in 1912, was built of wood with a masonry shell and many crevices for fire to slip through.

In late afternoon, the Virginia Department of Health issued an advisory, asking nearby residents to try to avoid the smoke.

As darkness began to fall, the fire was considered under control, and crews planned to stay on the scene to keep putting out hot spots and watching the building next door.

Today will be the earliest investigators can get in to try to figure out the cause - if the building is safe enough to enter. The structure will probably have to be demolished, fire officials said.

"There will be companies here all night," Battalion Chief Audie Ferris said. "But I feel lucky. If it had gotten into the second building, it would have gotten into the third. They did a hell of a job."